1. Field of the Invention
The present invention relates to operational amplifiers generally and more particularly to a high voltage integrated circuit operational amplifier.
2. Description of the Prior Art
In high voltage integrated circuit amplifiers, the components have to be constructed to withstand the voltage across the device and, therefore, will be quite large to allow for depletion layer spreading. This is even more severe in the case of lateral PNP transistors, where the large base width results in low current gain of the transistor and high substrate injection along with the degraded frequency response.
Various operational amplifiers of the prior art are known, however, without the capability of withstanding a high voltage input on an integrated circuit VLSI chip. By way of background, U.S. Pat. Nos. 3,660,773; 4,135,162 and 4,232,273 are illustrative of known operational amplifiers and power amplifiers. Additionally with respect to U.S. Pat. No. 4,135,162, a known current mirror circuit is described. IBM Technical Disclosure Bulletin, Vol. 20, No. 2, July, 1977, in an article by R. C. Jaeger entitled "High Performance Differential Amplifier Input Stage" also describes a known current mirror configuration.